Conversion – Instantaneous PPFD to Integrated PPFD

Souce: Apogee Instruments

Most light meters measure the instantaneous photosynthetic photon flux density in µmol m^-2 s^-1 and yet plant growth is determined by the integrated daily photosynthetic photon flux density in mol m^-2 d^-1.

Here is how to convert from µmol m^-2 s^-1 to mol m^-2 d^-1 when using electric lights.

There are 3600 seconds in an hour. If the electric light output is constant, the instantaneous PPFD can be added up (integrated) over an hour.

Therefore 1 µmol m^-2 s^-1 = 3600 µmol m^-2 h^-1.

This must be divided by a million (1,000,000) to convert from micromoles to moles: 3600 µmol m^-2 h^-1 = 0.0036 mol m^-2 h^-1.

If the electric lights are on continuously (24 hours), the hourly PPFD must be multiplied by 24 to get the daily PPFD: 0.0036 mol m^-2 h^-1 = 0.0864 mol m^-2 d^-1.

There are 86,400 seconds in a day (3600 x 24 hours) so the daily PPFD can be calculated directly from the instantaneous PPFD from the following equation: µmol m^-2 s^-1 multiplied by 86,400 and divided by 1,000,000 = mol m^-2 d^-1.

So: 1 µmol m^-2 s^-1 = 0.0864 mol m^-2 d^-1 with continuous light

These conversions are accurate only under electric lights. The integrated daily PPFD from sunlight changes during the day so a single measurement cannot be used to estimate daily PPFD.